God told Moses, Moses, don’t you know that Pharaoh sees you as a god? He thinks of Aaron as your prophet, man, I promise. Really. And I command you to go to Pharaoh and tell him to let the Hebrews go. It won’t work of course. I’ll see to that. I feel like getting my smite on here in Egypt. But go tell Pharaoh anyway so I can start the smiting. Anyways, when Pharaoh wants evidence that you come from God, do the staff trick and see if that don’t blow his mind.
So Moses and Aaron wen to Pharaoh and told him to let the Hebrews go. When Pharaoh looked bored and vaguely annoyed, Aaron was all, hey, check this out! and threw down the magic staff, and it turned into a snake. Pharaoh yawned and waved to his court magicians, who all threw down their staffs, which also turned to snakes. So now there were all these snakes writhing about, but before anyone could try to catch them so they’d turn back into staffs, Aaron’s staff-cum-snake ate the other three. I guess his must have been a king snake or something.
Despite the eating, Pharaoh still wasn’t convinced, so God told Moses to ambush Pharaoh the next day when Pharaoh went down to the Nile to bathe. At the riverbank, Moses was all, let the Hebrews go, Pharaoh, or else. Pharaoh just gave Moses a hard look and turned to step into the river when, behold, Aaron waved the magic staff over it, and it turned into blood! Pharaoh was all, ok, ew, thanks guys. Magicians! And they began turning water into blood too, until there was no water left in Egypt. Pharaoh was all, whatevs. I’ll just drink wine. But the common folk spent the week digging new wells looking for water and all the fish started dying and rotting and stinking.